1. Field of the Invention
The invention generally relates to variable format printing devices. More particularly, the invention pertains to microprocessor-controlled printer peripheral units using thermal printhead dot matrices and heat-sensitive paper as the print medium for producing documentation of data received from a host system.
2. Description of the Prior Art
Printing peripherals are presently available for host systems requiring the production of printed documentation. Such a host might comprise, for example, a power monitor, gaging station, or process controller. The documentation printed may consist of alphanumeric characters, or graphs.
Typical applications require a printer that is physically small and durable and that prints on two-inch wide paper. Reports generated by the printer could be entered into a daily operations log or passed along a production line with the parts to which the report pertains. Commonly, the printer would be mounted in a vertical panel with the paper feeding out and down the face of the panel. In this configuration, the print would likely comprise a data log with any printed characters appearing upright. On the other hand, a text printer mounted in a vertical panel would typically generate characters positioned such that when the paper tape would be inverted, the message would read as printed top to bottom.
Because such peripheral printers use narrow paper (e.g. 2 inches), graphical dot displays are best generated with the time axis running the length of the paper. Labels and messages printed on the graph's axis should likewise run vertically with the direction of paper feed. A graph produced in this way is commonly called a strip chart.
Most printer peripherals have limited and fixed character sets governed by print hammers or other mechanical apparatus, which causes resultant print documentation to be cryptic and ambiguous. Furthermore, the typical printing peripheral is optimized for a specific type of printing or for graphing and has insufficient versatility to simultaneously handle both types of documentation.
When a printer with only an alphanumeric character set generates a strip chart graph, the resultant output is comprised of data points represented by characters having very low resolution. Also, many chart recorders of the prior art have no alphanumeric capability for producing labeled charts or graphs.
Further prior art peripheral printer deficiencies involve interfacing inflexibility between printer and host. The typical prior art printer peripheral accommodates a single type date communication interface, or worse yet, leaves all interfacing details to the user.
Finally, no chart or strip chart recorders known in the art accept both analog and digital data as a standard feature without the need for circuitry changes in the printer controller.